Lighting device for a surgical microscope

ABSTRACT

The invention relates to an illumination device for a surgical microscope comprising a main objective lens ( 1 ) surrounding a main optical axis ( 6 ) and an illumination optical system ( 2 ) having a light source ( 3 ). Two prisms ( 4, 5 ) are provided between the main objective lens ( 1 ) and the illumination optical system ( 2 ). During operation, the first prism ( 4 ) causes part of the light flow from the illumination optical system ( 2 ) to be deflected at a small angle to the main optical axis ( 6 ) and the second prism ( 5 ) causes another part of the light flow from the illumination optical system ( 2 ) to be deflected along the main optical axis ( 6 ). Both prisms ( 4, 5 ) are arranged next to each other. The light entry surfaces ( 7 ) of both prisms face the illumination optical system ( 2 ) in such a way that light flux can be independently adjusted for the two prisms ( 4, 5 ). This results in a compact design and a good light flux distribution.

CROSS-REFERENCES TO RELATED APPLICATIONS

The present application is the U.S. national phase under 35 U.S.C. 371of International Application No. PCT/EP99/02151 filed Mar. 25, 1999claiming priority of Swiss Patent Application No. 1078/98 filed May 13,1998.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention concerns an illumination system for a surgical microscope.Quite varied illumination systems are known in microscopy. Illuminationis a particularly difficult subject in surgical microscopy, and, there,especially, in ophthalmology. That is because optimal illumination canbe critical for surgical success and also because the light intensityunder the microscope cannot be made as high as might be desired becauseof danger to the tissue.

2. Description of the Related Art

German Patent C2-40 28 605 and its family member, U.S. Pat. No.5,126,877, present a known illumination system. A still olderillumination system which works well, was marketed in 1985 by theapplicant's predecessor company as “0° Illumination System” (see theWild Heerbrugg AG brochure M1 668d-X.85 of Oct. 1985).

In this design, the entire light beam is deflected from an illuminationoptical system with its lamp by a first prism, from a perpendicular tothe optical axis of the main objective of the microscope into an obliquebeam at a small angle (e. g., 6°) from the optical axis. This is themain illumination of the surgical field. But, to get the “0°illumination” particularly desired for eye surgery because of the “redreflection” which it produces, a transparent disk parallel to theprincipal plane of the main objective is placed between the first prismand the main objective. This disk can be rotated about the main axis.The disk carries a second prism, which is relatively narrow incomparison with the first one. This second prism moves part of the lightbeam diverted by the first prism into the main axis by means of twoapproximately parallel mirror surfaces.

Thus, rotation of the mirror can optionally add “0° illumination” tostandard illumination at a small angle to the main axis. That processreduces the light flux of the standard illumination in proportion to thelight flux which it uses. Theoretically, it is possible to control thedistribution of the light by the angular position about the main axis.

As well proven as this known design is, there has been a great desirefor newer solutions which work without rotating disks. The solution ofthe German C and U.S. patents cited was noted initially as one suchsolution.

A significantly more recent design is reported in Japanese PatentApplication 9-105866. It is somewhat comparable with the old “0°Illumination” of the predecessor of the applicant, in that it has, belowthe first prism, a second prism with two mirror surfaces, but it doesnot rotate about the main axis. This design gives a fundamentallyconstant division of the light flux between the 0° portion and thelarger portion that is permanently incident at a small angle. Apparentlyit is possible to reduce the joint light flux by a diaphragm which canbe inserted into the beam path of the illumination optical system.

This Japanese design has in common with the “0° Illumination” that twoprisms are placed in succession, so that both require a certain distancein front of the main objective. In addition, control of the light fluxin the main axis region necessarily changes the light flux which isincident on the object at a small angle.

One of those effects, and preferably the other also, are intended to beavoided according to the invention.

The object of the invention, then, is to provide a compact illuminationsystem with at least one oblique (with respect to the main axis) lightflux and at least one parallel light flux, so that as much as possiblethe two light fluxes can be controlled independently of each other.

SUMMARY OF THE INVENTION

This object is attained, for the first time, by an illumination systemaccording to the present invention. The illumination system generallycomprises an illumination means for providing an illumination beam oflight along an illumination optical axis, and a plurality of prismslocated to receive and divert respective portions of the illuminationbeam through the objective lens of the microscope either along the mainoptical axis of the objective lens or at a small angle relative thereto.

An elegant solution with symmetric illumination of the object includes acentral prism for diverting a portion of the illumination beam along themain optical axis, and a pair of prisms located on each opposite side ofthe central prism for diverting portions of the illumination beam at asmall angle to the main optical axis, wherein the three prisms have acombined light entry surface area facing the illumination beam thatessentially admits the entire illumination beam when unblocked.

The present invention gives a small height, as the prisms are now sideby side. It also assures that the light entry areas of the two prismscan be supplied with a partial flux of light independently of eachother, so that each of these partial light fluxes can be controlledindependently of the other.

Placing an adjustable diaphragm between the illumination optical systemand at least one light entry surface of at least one prism presents anexample of one such potential for regulation. Adjustable diaphragms suchas an opaque disk with windows which can be selectively placed so as toallow the illumination beam to enter different light entry surfaces todifferent extents, as needed, are simply adjustable diaphragms. An LCDwhich, under electronic control, allows freely selectable portions toenter the light entry surfaces is a particularly user-friendlydiaphragm. LCDs can be used as gray filters by selective darkening. Onthe other hand, electronically stored window shapes can be used toprovide quite varied illumination adjustments.

The invention is not limited to these stated diaphragms, though. It caninstead be equipped with any known or novel system for light controlwithout losing its essential feature, the flat, compact design and theability to control independently.

In a particular embodiment and possibly an alternative to thosedescribed previously, at least one light-interrupting part is positionedat at least one of the reflective surfaces of the prisms, in such a waythat the light-interrupting part can be moved or swiveled withelectronic means, or can be electro-optically controlled so as torefract the total reflection. It can reasonably be used alternatively oreven in combination. If needed, it also leads to an improved and evenmore symmetric illumination.

The term “light-interrupting part” is understood to mean any element inwhich total reflection is eliminated at the contact site when in contactwith a total reflection surface. They could, for example, be prisms,glass plates, or even certain, possibly non-transparent, plastic ormetal plates or liquids. This particular embodiment provides not onlythe possibility for light control, but also the possibility for dividinga light flux for use of another optional mirror element to produceanother illumination beam at an angle to the main axis. There is anotherpreferred embodiment in which only the “0° Illumination” is controlledby using the interruption of total reflection or, in case the light fluxis diverted out of the second prism, it is directed to another obliqueillumination beam independent of the first oblique illumination beam.

According to the invention, a means for controlling the color of thelight can also be provided, independently of, or in addition to, thelight flux regulation.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is explained in more detail with the drawing. The drawingshows:

FIG. 1: a plan view of the essential elements of the invention;

FIG. 2: an expanded side view with a schematic illumination opticalsystem and the main objective;

FIG. 3: an example of an aperture disk according to the inventions

FIG. 4: a partial side view showing a variation of the presentinvention, wherein a light-interrupting part thereof is a glass plateshown in cross-section in the view; and

FIG. 5: a partial side view showing a variation of the presentinvention, wherein a light-interrupting part thereof is an opaquecomponent shown in cross-section in the view.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The figures are described together. Identical reference symbols indicateidentical parts. Identical reference symbols with different indicesindicate parts with identical or similar functions.

A two-part first prism 4 a and 4 b is at the sides of a second prism 5.They can, for example, be cemented together. Each prism has one lightentry surface 7, which faces an illumination optical system 2. A lightsource 3 is shown as an example. It could quite well also be a lightguide. The division of prism 4 into two parts is not essential, butpreferred, because that gives good symmetry of the illumination. Thearrangement can also be asymmetrical.

An adjustable diaphragm 8 can optionally be placed between theillumination optical system 2 and the light entry surface 7. Thediaphragm can, for instance, appear as shown in FIG. 3. There one cansee windows 11 a-11 d, which can be placed, as desired, in front of thelight entry surface 7. In FIG. 3, window 11 d is placed in front of thelight entry surface 7 c of the second prism, so that in this case only0° illumination is active at fall intensity. Both of the first prismparts 4 a and 4 b get practically no light flux. If one were to turn thewindow 11 d somewhat farther, that could produce a division of the lightflux between the light entry surface 7 c and one of the two light entrysurfaces, 7 a or 7 b.

Windows 11 b are provided as an obvious alternative. They allow completecutoff of the 0° illumination with simultaneous full illumination of thefirst prism 4. Windows 1 la allow full illumination of all the prisms 4,5; and window 11 c allows full illumination of prism 5 with simultaneousreduction of the illumination to the first prism 4.

Prism 4 a,b, could also be designed throughout as a single piece, sothat prism 4 covers the entire entry surface 7 a,b,c. Then prism 5 wouldbe a narrower prism cemented to the hypotenuse of prism 4. Obviously,prisms 4 and 5 could also be made as a single one-piece prism.

Independently of diaphragm 8, a slidable prism 10 is also provided as alight interruption part. Its plane surface can be slid along the totalreflection surface 9 of the second prism 5, with automatic drive means13 preferably being provided for moving or rotating prism 10. Althoughthis is not shown in detail, it can, for instance, be pressed againstsurface 9 by a spring. Because of the interruption of the totalreflection, part of the light flux from the second prism 5 is notreflected through the main objective 1, but is taken out from the secondprism 5 by the light interruption part 10. As shown in FIG. 4, thelight-interrupting part can also be embodied as a glass plate 10′. Inanother variation illustrated at FIG. 5, the light-interrupting part isembodied as an opaque component 10″, such as a plastic or metal plate.

In this case, a liquid film, especially an oil film, on the contactsurface could be helpful. In a variation, not shown, that could resultin destruction of the light, for instance, if the right surface of thelight interruption part 10 is colored black, or if this surface istransparent, but directed toward a black interior coating of themicroscope tube.

The total reflection can also be interrupted, within the meaning of theinvention, by electro-optical layers (e. g., LCD, crystal, orvapor-deposited coatings) between the two prisms. These layers could, tothe extent that they can be selectively activated electronically, makethe desired areas totally reflecting or nonreflecting.

In the present example embodiment, though, this surface is directedtoward another mirror surface 12, which redeflects the deflected lightflux through the main objective 1 onto the object at a small anglerelative to the main optical axis 6 of the objective 1. If necessary,the other mirror surface could also be adjustable so as to affect theangle of reflection, but that is not shown in detail.

What is claimed is:
 1. An illumination system for a surgical microscopefor illuminating an object to be viewed, said microscope having a mainobjective lens aligned on a main optical axis, said illumination systemcomprising: illumination means including a light source for providing anillumination beam of light along an illumination optical axis; and threeprisms placed between said main objective and said light source, each ofsaid three prisms including a light admission surface, said three prismsbeing arranged side-by-side such that said light admission surfaces arein a single plane intersected by said illumination optical axis, two ofsaid three prisms operating to divert part of said illumination beam ata small angle to said main optical axis of said objective lens and aremaining one of said three prisms operating to divert another part ofsaid illumination beam along said main optical axis; wherein said threeprisms have a combined light admission surface area facing saidillumination beam.
 2. The illumination system according to claim 1,wherein said two of said three prisms are placed at opposite sides ofsaid remaining one of said three prisms to produce symmetricillumination of said object.
 3. The illumination system according toclaim 1, further comprising an aperture diaphragm placed between saidillumination means and at least one light admission surface of at leastone of said three prisms.
 4. The illumination system according to claim3, wherein said aperture diaphragm is an opaque disk including aplurality of light-transmitting windows that can be selectively placedin said illumination optical axis to control light flux enteringrespective light admission surfaces of said three prisms.
 5. Theillumination system according to claim 3, wherein said aperturediaphragm is an LCD electronically controlled to allow selectableportions of said illumination beam to enter respective light admissionsurfaces of said three prisms.
 6. The illumination system according toclaim 1, wherein each of said three prisms includes a reflective surfacefor diverting an incident part of said illumination beam, and saidillumination system further comprises a light-interrupting elementassociated with at least one of said reflective surfaces forinterrupting total reflection at said associated reflective surface. 7.The illumination system according to claim 6, further comprisingautomatic means for moving said interrupting element.
 8. Theillumination system according to claim 6, wherein saidlight-interrupting element is electro-optically controlled.
 9. Theillumination system according to claim 6, wherein saidlight-interrupting element is a transparent prism.
 10. The illuminationsystem according to claim 6, wherein said light-interrupting element isa glass plate.
 11. The illumination system according to claim 6, whereinsaid light-interrupting element is an opaque component.
 12. Theillumination system according to claim 6, further comprising anotherreflective surface for diverting rays emerging from saidlight-interrupting element at an angle relative to said main opticalaxis.
 13. The illumination system according to claim 6, wherein saidlight-interrupting element is associated with said reflective surface ofsaid remaining one of said three prisms.
 14. The illumination systemaccording to claim 1, further comprising a color-selecting filter meansplaced between said illumination means and at least one light admissionsurface of at least one of said three prisms for controlling the colorof said illumination beam.